Hey,
It is a very good option to save for a Fukurokumaru's Deals as you said, to acquire an additional ninja from there. What concerns the different treasures, make sure to not invest your scrolls towards the Kage treasure, it's not really worth anymore unless that will be your last option later on. The lightning treasure is really okay and solid overall for the start and it will be helpful as well. The Great Ninja War Treasure has mostly the top priority in the treasure, as the super rares are really good in general.
An option would be to keep playing with mains as position one using teams such as shark bomb teams till you acquire an additional ninja such as Naruto Six Paths, that can stand on the field alone and help you in general for a long time in the game, in any mode & invest your scrolls towards the Great Ninja War treasure instantly.
Another one would be to draw in the lightning treasure of course and acquire all the ninjas from there, since you'll get them easy with about 210 draws. Both options are not wrong and the lightning treasure is giving you a fast option and one team which works really good at the start. You should avoid for now the Edo Jinchuriky treasures, as all of their ninjas in there do really need specific ninjas to build a team with and additionally, the chance of acquiring a super rare is always 50%, regardless if you have it or not from there.
Hope that helps and if you got any other questions, feel free to ask 
Minato Edo is not really a issue, but Minato Jonin is a deadly opponent for the lightning treasure team xD. About water main teams, you can build infinity of these, you just place three support ninjas and you are ready to go. An example :
Ninjas that can work here are any that can buff either your water main or your whole team with defense/resistance for example, cleanse, heal, etc. Han and Madara 5 kage are great combinations with her, since you can remove buffs from your opponent. In that case, you are playing with Aura support (Ninjas that buff your team when they are alive on the field, example : Sai Suit, Naruto Suit, Chiriku)
You can replace Sakura with any other ninja that can heal for example, buff, etc. Also, yeah, water main requires initiative to reach the maximum potential and be more effective, however, there are strategies and support ninjas which c*so give you a hand in case you lack that. Example, Edo Itachi. Minato Edo will have a three round CD and that's his weakness basically.
Play around with all the supports, water main just does not get boring because almost everything works with her at the start 
Also you are welcome! 
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